Climate Zone Migration: What You Can Now Grow in Your Garden
Has your USDA hardiness zone changed? The 2023 map update shifted about half the US into warmer half-zones. Here’s exactly what that means for your garden — and which plants you can now reliably grow.
Something has been shifting quietly in American gardens over the past decade. Plants that used to reliably die every winter are surviving. Lavender that should have been marginally hardy in Zone 6 is now returning lush and well-branched in spring. Crepe myrtles that gardeners once grew as annuals in northern states are putting down permanent roots. If you’ve noticed your garden becoming more forgiving of plants that used to struggle, you’re not imagining it — and the USDA made it official in November 2023.
The 2023 Plant Hardiness Zone Map update confirmed what many gardeners had already observed on the ground: roughly half of the United States has shifted into a warmer half-zone than it occupied on the previous 2012 map. That half-zone shift represents an increase of up to 5°F in the average annual minimum winter temperature — enough to move borderline plants firmly into the “reliable perennial” category and open the door to species that were previously off-limits entirely. This guide explains exactly what changed, which zones are most affected, and which plants you can now realistically trial in your garden. To time your new plantings for success from the first season, pair this guide with our year-round planting guide.
Has My Hardiness Zone Changed? What the 2023 USDA Update Found
The USDA Plant Hardiness Zone Map is the standard reference for cold hardiness across the US. Each zone is defined by a 10°F band of average annual extreme minimum temperature, and each zone is split into two half-zones (A and B) representing 5°F increments. Zone 6b, for example, has average annual extreme minimum temperatures of 0°F to −5°F. If your zone number changes, your average coldest winter night has become meaningfully warmer.
The 2023 update was the first since 2012 and represents the most data-rich map ever produced. The USDA Agricultural Research Service incorporated temperature readings from 13,412 weather stations — up from 7,983 in the previous version — and used data from the 1991–2020 period rather than the older 1970s–2005 baseline. The result: about half the country shifted into the next warmer half-zone. The other half stayed the same.
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How to find your new zone: The interactive USDA PHZM tool at planthardiness.ars.usda.gov lets you enter any US zip code and instantly see your current assigned zone. Check this first before assuming your zone has or hasn’t changed — the shifts were not uniform across the country, and some regions saw larger movements than others.
The half-zone shift is not dramatic on paper, but it translates meaningfully in the garden. A gardener who was in Zone 5b (average minimum −15°F to −10°F) and is now in Zone 6a (−10°F to −5°F) has gained 5°F of winter cold protection. That 5°F gap is the difference between a plant surviving winter and dying back to the roots — or between dying back and freezing outright.
What a Zone Change Actually Means for Your Garden
Zone numbers represent one thing only: the average annual extreme minimum temperature. They say nothing about summer heat, humidity, rainfall, soil type, or growing season length. A gardener in Zone 7a in Seattle and a gardener in Zone 7a in Charlotte, North Carolina share the same hardiness zone but grow in almost entirely different conditions.
With that caveat clearly in mind, a warmer zone assignment has two practical effects:
Borderline plants become reliable. Many plants rated for Zone X are genuinely hardy in Zone X in a typical year, but killed by the occasional severe winter that dips colder than average. When your minimum temperatures rise, those severe dip winters become less frequent and less extreme — borderline plants survive two winters out of two instead of one out of three.
Zone X+1 plants become triable. Plants rated one zone warmer than your previous zone rating were simply off-limits. In your new zone, they sit at their rated threshold — and with good site selection and the first-winter protection described at the end of this guide, a significant proportion of them establish permanently.
What a zone change does not do: it doesn’t extend your last spring frost date or first fall frost date significantly, it doesn’t change summer heat load, and it doesn’t guarantee that a harsh cold snap won’t still damage newly-rated plants in an anomalous winter. The zone is an average, not a promise.
New Opportunities for Zone 5 Gardeners
Zone 5 gardeners who have shifted to Zone 5b or Zone 6a gain access to a meaningful set of plants that were previously only possible with significant protection or luck.
Hydrangeas — expanded reliable variety range: Bigleaf hydrangeas (Hydrangea macrophylla) have been notoriously unreliable in Zone 5 — the plants often survive but the flower buds, formed the previous summer, die in cold winters, resulting in foliage with no blooms. The half-zone warming reduces the frequency of those bud-killing cold snaps significantly. Reblooming varieties like ‘Endless Summer’ and ‘Incrediball’, which produce blooms on both old and new wood, now have a much stronger track record in the upper Midwest and New England. For full planting guidance, variety selection, and cold protection techniques specific to this zone, see our guide to growing hydrangeas in Zone 5.
Hardy fig varieties: Chicago Hardy fig (Ficus carica ‘Chicago Hardy’) is rated to Zone 5 and now has genuine survival prospects without the extensive wrapping and mulching that was previously essential. Even if the top growth dies back in a cold snap, established Chicago Hardy figs typically regenerate from the roots and fruit on new wood within a single season.
Japanese maples — broader variety selection: Many of the most ornamental Japanese maple varieties (Acer palmatum cultivars) are rated Zone 5b to Zone 6. Gardeners who were solidly in Zone 5a now have access to a wider palette, particularly the dissectum (lace-leaf) types that were previously marginal.
Butterfly bush (Buddleja davidii): Rated Zone 5 in most cultivars, butterfly bush was reliably hardy across much of the zone but often died back hard in severe winters, returning slowly in spring. In a warmer Zone 5b, die-back becomes less common and spring growth begins weeks earlier, extending the effective bloom season meaningfully.
What Zone 6 Gardeners Can Now Trial
Zone 6 is where the zone migration impact is perhaps most visible. Gardeners in the mid-Atlantic, lower Midwest, and transition-zone areas who have moved from Zone 6a to Zone 6b are now sitting at the threshold of genuinely exciting plant territory.
Lavender — now a reliable perennial: English lavender (Lavandula angustifolia) is rated Zone 5–8, but in practice it struggled at the cold end of Zone 6 — surviving most winters but dying out after hard winters or in poorly-drained soils that froze solid. In Zone 6b, English lavender planted in well-drained, slightly alkaline soil in a sunny position now performs as the reliable, long-lived perennial it’s meant to be. For variety selection, planting depth, soil amendment, and first-winter care in your zone, see our dedicated guide to growing lavender in Zone 6.
Roses — more variety options and less winter damage: Many of the most desirable rose varieties — hybrid teas, climbers, and old garden roses — are rated Zone 6 or 6b. Gardeners who were firmly in Zone 6a found that these varieties technically survived but required cane protection and mounding to reliably make it through cold winters. In Zone 6b, winter protection needs drop significantly, and the more tender climbing and old garden varieties become reliable garden plants without wrapping. Our Zone 6 rose growing guide covers the varieties that perform best in these conditions and when to stop deadheading to allow hips to harden before frost.
Crepe myrtle (Lagerstroemia): Crepe myrtle is rated Zone 6–9 in cold-hardy varieties like ‘Natchez’ and ‘Dynamite’. In Zone 6a, these survived but often died back significantly each winter, spending energy on regeneration rather than bloom. In Zone 6b, die-back becomes partial or minimal, and the shrubs develop the permanent woody framework that produces the best flower display. Expect a noticeable improvement in bloom quality by year three in a warmer zone position.
Artichokes as overwintering perennials: Globe artichokes (Cynara cardunculus var. scolymus) are often grown as annuals in Zone 6, but they’re perennial to Zone 6b with crown mulching. A 4–6 inch layer of straw mulch over the crown after frost, removed in early spring, is now sufficient to carry established plants through winter in Zone 6b — eliminating the annual replanting cost and producing larger harvests from more mature plants.
What Zone 7 Gardeners Can Now Trial
Zone 7 gardeners moving from 7a to 7b gain access to genuinely subtropical plants that were previously only possible in containers brought indoors.
Lavender as a permanent landscape plant: In Zone 7b, all species of lavender — English, French (Lavandula dentata), and Spanish (Lavandula stoechas) — now overwinter reliably outdoors. French and Spanish lavender, with their longer bloom seasons and more ornate flower forms, are rated Zone 7–11 and were genuinely marginal in Zone 7a. In Zone 7b they establish as permanent, low-maintenance landscape plants. See our guide to growing lavender in Zone 7 for variety comparisons across all three species and how to extend the bloom season into early fall.
Roses — expanded climbing and old garden variety selection: Zone 7b opens up the full range of climbing roses, including some of the most spectacular large-flowered climbers that were marginal in Zone 7a. Once-blooming old garden roses like Maiden’s Blush, Cardinal de Richelieu, and Charles de Mills — which require a period of cold dormancy but dislike severe freezes — perform particularly well in Zone 7b’s reliable mild winters. Our Zone 7 rose guide covers the full variety spectrum now available, from disease-resistant shrubs to heirloom climbers.
Fig trees as permanent landscape features: Brown Turkey and Celeste figs (rated Zone 7–9) now overwinter without protection in Zone 7b, developing into multi-stemmed shrubs or small trees that fruit heavily on established wood. In Zone 7a these varieties survived most winters but died back sufficiently to reduce fruiting wood, requiring patient regeneration each spring. In Zone 7b, a fig planted today becomes a productive, permanent landscape tree.
Camellia and gardenia (sheltered positions): Camellia japonica is rated Zone 7–9, and in Zone 7b planted against a south-facing wall or in a sheltered courtyard it now overwinters without protection in most years. Gardenia jasminoides (rated Zone 7–11) is more marginal but achievable in the most protected south-facing positions in Zone 7b — the type of microclimate shown in the image below.
The Vegetable Garden: What Zone Warming Changes
Hardiness zones primarily describe ornamental plant survival, but warmer winter minimums also shift the effective growing season in ways that matter for vegetables.
The tomato season gets longer at both ends. The last spring frost date moves earlier by days to weeks in warmer-shifted zones, and the first fall frost date arrives later. For tomato growers, this is the most significant practical change: more days between transplant-out and first frost means more ripe tomatoes from indeterminate varieties, and the ability to try larger-fruited varieties that need a longer ripening window. Our guides to growing tomatoes in Zone 6 and growing tomatoes in Zone 8 cover the variety selection and timing adjustments that apply specifically to those zone conditions.
New crops become viable in warmer-shifted zones. Sweet potatoes, which need 90–120 days of warm soil (above 65°F) to produce well, become reliably productive in zones that previously only barely reached the required soil temperature window. Okra, rated Zone 7–11, now reliably produces in Zone 6b gardens that previously just barely got hot enough for it. Yard-long beans, cowpeas, and lemongrass become realistic additions rather than curiosities in zone-shifted Zone 6 and 7 gardens.
Overwintering vegetables expand in Zone 7 and 8. Gardeners in Zone 7b can now reliably overwinter spinach, kale, chard, and mache (corn salad) without row cover in most winters. Cold frames and low tunnels — which previously kept these crops alive at marginal temperatures — now function as genuine production tools rather than survival systems, allowing continuous harvest rather than just plant preservation.
Microclimates: The Factor That Outweighs Your Zone Number
Your assigned zone describes the average coldest conditions across a broad geographic area. Your actual garden contains multiple microclimates that can be significantly warmer or colder than that average — and understanding those microclimates is more valuable than any zone-map update.
South-facing walls: A masonry or brick wall facing south absorbs heat throughout the day and radiates it back through the night, keeping the air immediately adjacent 5–10°F warmer than the open garden during the coldest winter hours. A Zone 6b gardener with a south-facing brick wall has a planting position that effectively functions as Zone 7a or 7b. This is where to trial the most borderline plants — a camellia, a gardenia, or a tender climbing rose — before committing to a full bed installation.
Urban heat island effect: Gardens in dense urban neighborhoods can run 2–5°F warmer than the official zone for their zip code, simply due to the retained heat of surrounding buildings, pavement, and infrastructure. Urban gardeners are often effectively one half-zone warmer than their official classification suggests.
Cold air frost pockets: Low points in the garden — the bottom of a slope, a depression surrounded by dense plantings, or any area where cold air drains and collects — can be 3–5°F colder than the surrounding garden on still, clear nights. These are the worst positions for borderline-hardy plants, regardless of what the zone map says. A plant that survives in the open garden may consistently die in a frost pocket.
Identifying your microclimates: Place a digital min/max thermometer in the open garden and a second one near your south-facing wall or other sheltered position. Track the minimum temperature on several consecutive cold nights through winter. Within one season you’ll have a precise picture of what each part of your garden actually experiences — far more useful than any map-based zone number.
What Zone Migration Doesn’t Fix
It’s worth being clear about the limits of zone warming so expectations remain realistic.
Summer heat and humidity stay the same. The USDA Plant Hardiness Zone Map describes only winter cold. A gardener in Zone 7b Atlanta and a gardener in Zone 7b coastal Oregon are in the same hardiness zone but face completely different summer conditions. Plants that dislike summer heat and humidity — like many English perennials — won’t perform better in a warmer zone if the summers were already their limiting factor.
Late-season cold snaps still happen. Zones represent 30-year averages. An anomalous cold winter in a warmer-shifted zone can still kill plants that the zone says should survive. The 2021 Texas freeze is the most dramatic recent example: Zone 8–9 plants died in an event far outside normal zone parameters. Zone migration improves the odds; it doesn’t eliminate risk.
Rainfall patterns and soil conditions are unchanged. A plant that needs consistently moist soil doesn’t become easier to grow just because winters are warmer. Zone is one dimension of plant suitability — match your plants to all of your garden’s conditions, not just its hardiness number.
How to Trial New Plants in Your Newly Warm Zone
The most common mistake when trialing zone-edge plants is committing too many plants too quickly before knowing whether your specific garden can support them.
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Start with one or two specimens. Buy one crepe myrtle, one fig, one camellia. If it survives two winters, add more. If it dies, you’ve learned something valuable about your site without significant cost.
Plant in your warmest microclimate first. That south-facing wall, the sheltered courtyard, the south slope that drains cold air away — these are where borderline plants have the best chance of establishing before you try them in more exposed positions.
Fall planting gives woody plants a root advantage. Planting trees and shrubs in fall allows them to establish a root system before winter, so they come into their first spring with more capacity to handle any cold stress. Spring-planted borderline plants face a double challenge: establishing roots and surviving their first winter simultaneously.
Protect the first winter, evaluate the second. Apply a 3–4 inch layer of mulch over the root zone in late November for the first winter. By the second winter, the plant’s root system is established enough that you can remove the protection and see how it performs unassisted. This gives you a fair trial of the plant’s true hardiness in your conditions, rather than a protected nursery situation.
Track your minimum temperatures. A min/max thermometer recording actual overnight lows at your planting site is the single most useful tool for understanding what your garden really experiences. Two winters of data will tell you more about your microclimate than any zone map.
Frequently Asked Questions
Has my hardiness zone changed with the 2023 USDA update?
About half the US shifted into the next warmer half-zone in November 2023. To find out specifically whether your location changed, enter your zip code at the USDA Plant Hardiness Zone Map tool at planthardiness.ars.usda.gov. The interactive map shows both your current zone and allows comparison with the previous 2012 map.
What does a half-zone change actually mean in practice?
Each half-zone represents 5°F of average annual minimum temperature. Moving from Zone 6a to Zone 6b means your average coldest winter night is now expected to stay above −5°F rather than dipping to −10°F. In practice, this means fewer winters with severe cold snaps, more consistent survival of borderline plants, and the ability to trial plants rated one half-zone warmer than before.
Can I now grow plants rated one full zone warmer than my old zone?
A half-zone shift typically gives reliable access to plants rated to the top of your new zone. Plants rated a full zone warmer (10°F warmer minimum) are still risky for open-garden planting, but become viable in sheltered microclimates — particularly south-facing walls or sheltered urban courtyards that already run significantly warmer than the ambient zone temperature.
Is the zone change permanent, or could it shift back colder?
Zone maps represent 30-year averages of recorded temperatures. Future maps could shift in either direction depending on the temperature record of the next data period. However, the general trend of rising minimum temperatures across much of the US is consistent and well-documented. Planting decisions should account for the possibility of anomalous cold years even in a warmer zone.
My plants seemed to do better before I knew my zone changed — should I change what I grow?
Zone migration validates what observant gardeners were already noticing. If you’ve been successfully growing “borderline” plants, your microclimate was already warmer than the official zone indicated, or you were simply lucky during mild winters. The new zone assignment doesn’t require you to change anything — it just gives you the confidence to trial a few more ambitious plants without feeling like you’re ignoring the rules.
Sources
- USDA Agricultural Research Service — USDA Unveils Updated Plant Hardiness Zone Map (ars.usda.gov)
- University of New Hampshire Cooperative Extension — New 2023 USDA Hardiness Zones Explained (extension.unh.edu)
- USDA Plant Hardiness Zone Map interactive tool (planthardiness.ars.usda.gov)
